Wireless devices or terminals for communication are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server, such as server providing video streaming service, via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, computers, or surf plates with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
A cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area is served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. eNodeB (eNB), NodeB, B node, Base Transceiver Station (BTS), or AP (Access Point), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless devices within range of the base stations. The base stations and wireless devices involved in communication may also be referred to as transmitter-receiver pairs, where the respective transmitter and receiver in a pair may refer to a base station or a wireless device, depending on the direction of the communication. Two wireless devices involved in D2D communication may also be referred to as a transmitter-receiver pair. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to a wireless device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for communication with terminals. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE is controlled by the radio base station.
D2D communication is a well-known and widely used component of many existing wireless technologies, including ad hoc and cellular networks. Examples include Bluetooth and several variants of the IEEE 802.11 standards suite such as WiFi Direct. These systems typically operate in unlicensed spectrum.
Recently, D2D communications as an underlay to cellular networks have been proposed as a means to take advantage of the proximity of communicating devices and at the same time to allow devices to operate in a controlled interference environment. Typically, it is suggested that such D2D communication shares the same spectrum as the cellular system, for example by reserving some of the cellular uplink resources for device-to-device purposes. Allocating dedicated spectrum for D2D purposes is a less likely alternative as spectrum is a scarce resource and dynamic sharing between the D2D services and cellular services is more flexible and provides higher spectrum efficiency.
A transmission mode when sending data during D2D communication may e.g. be unicast wherein a specific UE is the receiver, multicast which also may be denoted groupcast wherein a group of UEs are receivers, and/or broadcast wherein all UEs are receivers.
With connectionless D2D communication, data can be sent from one device to another device without prior arrangement, thereby reducing overhead and increasing communication capacity which is crucial in emergency situations. The source device transmits data to one other device in unicast, or more than one other devices, in multicast, groupcast, or broadcast, without first ensuring that the recipients are available and ready to receive the data. Connectionless communication may be used for one-to-one or one-to-many communication, but it is particularly effective for multicast and broadcast transmissions and thus well-suited for broadcast and group communication
The connectionless communication may be realized, e.g., via Physical layer (PHY) unicast transmissions, multicast transmissions, groupcast transmissions or broadcast transmissions. With PHY broadcast transmissions, the transmissions may still be turned into unicast, groupcast, and/or multicast transmissions at higher layers. For example, in the Media Access Control (MAC) layer, multicast or even unicast addresses may be used. Or, alternatively, if using broadcast on both PHY and MAC, multicast or unicast Internet Protocol (IP addresses may be used at the IP layer.
In the seven-layer Open Systems Interconnection (OSI) model of computer networking, the PHY also referred to as layer 1 is the first i.e. lowest layer. The physical layer comprises basic networking hardware transmission technologies of a network. In the seven-layer OSI model of computer networking, MAC data communication protocol is a sublayer of the data link layer, also referred to as layer 2. The MAC sublayer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multiple access network that incorporates a shared medium.
One way to efficiently support D2D communication is to use a Scheduling Assignment (SA) followed by data transmission. As a prerequisite, the transmitter and receiver need to be configured with e.g., resource pool information such as time and frequency configuration, to be used for data transmission. When the transmitter needs to transmit data to the receiver it typically first sends a synchronization signal, which is later used as a time reference by the receiver. The next step is to transmit a scheduling assignment, followed by the actual data. It should be noted that the term transmitter refers to a transmitting device and the term receiver refers to a receiving device in the text herein.
SAs are control messages used for scheduling of D2D communication between devices. SAs are transmitted by a device such as a UE that intends to transmit D2D data and they are received by devices such as UEs that are potentially interested in such data. The SAs are transmitted on dedicated resources characterized by time and frequency, and is typically a sparse resource. SAs provide useful information that can be used by the receiver, e.g., to correctly decode a D2D data transmission associated to the SA, such as the resources for data transmission, the modulation and/or coding parameters, timing information, identities for the transmitter and/or receiver, etc. Typically, but not necessarily, SAs are transmitted prior to the actual data transmission, so that a receiver is able to selectively receive data based on the content of the SAs. The data transmissions scheduled by a SA are referred to as a transmission pattern.
By monitoring identities carried in the SA, Discontinuous Reception (DRX) is enabled in the receiver. For example, for multicast D2D communication, the identity in the SA identifies the multicast group. Thus a device such as a UE which is interested in receiving data of one or several multicast groups only need to check the SAs for the corresponding identities. When the UE receives an SA with an identity which corresponds to one of the multicast groups the UE is interested in, the UE may decode the data pointed out by the other information carried in the SA.
A method for providing redundancy in the scheduling assignments is known. For example, the same content may be transmitted by multiple SAs, and the transmitter may transmit only a subset of the redundant SAs, based on autonomous decisions or based on predefined patterns. This is to allow the receiver to periodically monitor the SA resources.
For SA, data and discovery transmission the transmitting UEs may need to select the transmission resources autonomously from a pool of available resources. The pool of available resources is shared by multiple potential transmitters that access it in a contention fashion. Different options are possible for the access algorithm including, e.g., random resource selection within the pool, energy-sensing, collision avoidance protocols, etc. It may be assumed that all UEs implement the same resource access algorithm.
The SAs and communication data for D2D are each transmitted on a common, shared resource pool which may be a common scarce resource pool, e.g. in time and/or frequency, as shown in FIG. 1. UE-A, UE-B and UE-C in FIG. 1 are transmitters. A UE may select the resource(s) to transmit the SAs and data using some rules or protocols. In case of high amount of traffic, these resource pools may become full and collisions may occur.